1. Field of the Invention
This invention relates to an engine for ships and more particularly to an open cycle Rankine engine on a ship which operates at the point of maximum specific horsepower.
2. Description of the Prior Art
In addition to the usual problems and restrictions besetting permanently installed powerplants such as requirements for fuel efficiency, cost, pollution control, and power, shipboard engines have special restrictions as to space and weight. Also, the conventional requirements for power and fuel efficiency are even more important than in other plants since not only is the cost of running the equipment involved, but the ability to patrol longer and to pursue the enemy more quickly. Therefore, efficiency and compactness produce enormous advantages which are not measurable in dollars and cents. Also, since the ship must be able to vary its speed, the engine must be able to retain its efficiency over a range of power loads.
In order to accomplish these many goals, various engines have been designed for shipboard and land-based powerplants. One system currently utilized for some Naval ships is a gas turbine based on a simple-cycle Brayton engine, designated the LM2500 and built by General Electric. While this system is generally reliable and efficient, it requires a very large and heavy eductor (stack) system which is a major handicap onboard a ship. In addition, this heavy stack forms the uppermost part of the ship adding a great deal of instability to the craft. Where the stack emerges through the decks it also occupies considerable space which would be better used for weaponry or other uses.
Many other systems have been proposed to improve such characteristics as fuel efficiency, power, total weight, or other factors. Many of such systems utilize Rankine or Brayton cycles and add regenerators or multiple serial compressors to increase performance. In some systems, water or steam is added to the products of combustion. Some examples of such prior art systems include powerplants shown in U.S. Pat. Nos. 3,335,565, 2,678,531, 3,449,908, and 3,461,667. While some factors are improved in these various systems, the basic problem of maximizing performance while minimizing weight and space remains.
Another concept using a dual-fluid cycle engine system has been proposed by Dah Yu Cheng in U.S. Pat. Nos. 3,978,661, 4,128,994, and 4,297,841. This device utilizes a Brayton cycle engine with steam injection operating at the point of maximum thermal efficiency. The steam is heated using a waste heat boiler and water may be recovered from the exhaust gases. While this system has improved characteristics over many prior art systems, it is still not a perfect powerplant system, especially for shipboard use. In particular, problems of fresh water procurement, stack weight, and space have not been addressed and partial load performance has not been as efficient as design point performance.